Inkers for printing plates which have achieved commercial acceptance generally comprise from two to four form rollers which are positioned in rolling engagement with a printing plate. Each of the form rollers is usually in rolling engagement with one or more vibrator rollers to which ink is applied by a multitude of rollers in a train of rollers of varying diameters arranged in pyramid fashion. Ink is delivered to the train of rollers over a ductor roller which oscillates into and out of engagement with a film of ink formed by a flexible doctor blade urged into engagement with the hard surface of an ink fountain roller by a multiplicity of ink keys.
The ink film formed on the ink fountain roller has been too thick and too irregular for application directly to a printing plate for quality printing. These inkers which include a multiplicity of rollers are intended to reduce the thickness of the ink film and to deliver a film of uniform thickness to the printing plate. However, since the ink film on each of the rollers is not totally replenished on each revolution of the form roller; image ghosting and ink accumulation and starvation is not completely eliminated. Thus, stripes and uneven ink distribution are produced on the product due to the ghosting and ink accumulation.
The multiple roller inkers require complex drive trains and are relatively expensive to purchase initially and to maintain thereafter.
Other types of inkers which have attempted to meter ink from a transfer roller to a form roller have utilized a doctor blade to remove all of the film of feedback ink from the form roller prior to replenishing the ink film. Since most form rollers are resilient, the contact of the doctor blade to the form roller surface scores the form roller and wears out the blade and roller causing an uneven film of ink.
The invention described herein addresses the problem of forming a thin film of newsprint type printing ink of low viscosity having substantially uniform thickness on a form roller and moving the film of ink into engagement with the image area on the printing plate while eliminating the trains of rollers in the inking system, eliminating the necessity for the consumption of excessive power and further reducing and eliminating numerous adjustments and areas of ghosting and ink accumulation which produce undesirable variations on the product being printed.
Devices of the type disclosed in U.S. Pat. No. 3,926,114 were devised to remove all the unused portion of ink and dampening fluid from the form roller prior to forming a new film of ink by metering the ink through a gap between the form roller and a transfer roller. There is considerable wear on the ink removal blade and the roller in this type of device. Also, it is extremely difficult to form an ink film which is sufficiently thin by using a doctor blade when metering newsprint ink.
Inking devices of the type disclosed in U.S. Pat. No. 2,240,762 employ rollers having cavities formed in the surface to meter ink onto a form roller for application to a printing plate.
A printing unit generally comprises two printing couples for applying ink to the web. If it is desired to print on both sides of the web in a single printing unit, the web is routed through the unit such that ink is applied to both sides. However, if it is desired to print two colors in the same unit on one side of the web, one of the printing couples must be reversed, from the direction used to print on both sides of the web, and the web is routed to print on one side. The reversal of the printing couple requires reversal of the rollers in the couple.